1. Field of the Invention
The present invention relates to a USB controller and a testing method of the USB controller.
2. Description of the Related Art
[Background Technique]
A communication standard, USB (Universal Serial Bus) 2.0, is widely used by various computer devices. The USB is one of several serial interface standards for connecting peripheral devices such as a keyboard and a mouse to a PC (a host PC) so that data communications between the devices and the PC may be carried out. The USB 2.0 offers high-speed communications, and is capable of connecting two or more devices to a hub that is connected to a port of the PC, which is an advantage over conventional interface standards. For this reason, the USB 2.0 has become a de-facto standard interface between PCs and peripheral devices. Here, the USB 2.0 is capable of providing a communication bit rate of 480 Mbps.
FIG. 1 shows a configuration example of a conventional USB controller 1, which is an IC (Integrated Unit) for controlling a device adopting the USB 2.0 specification. The USB controller 1 is for communicating according to the USB 2.0 specifications with a host PC that is not illustrated, and includes a PHY layer (PHYsical layer) 2, and a LINK layer 3. The PHY layer 2 is an analog unit for converting data and signals exchanged with the host PC; it includes a transceiver unit for serial communications of serial data with the host PC, a serial/parallel converter, and a data modulator/demodulator. The LINK layer 3 is a digital unit for recognizing an address of the data, an identification of the transmitting origin, boundaries of data, and the like, and includes a communication protocol unit for controlling a communication protocol. The functional units described above may be separately integrated into individual ICs, or alternatively, all of the functional units may be integrated into one IC.
When the PHY layer 2 and the LINK layer 3 are separately integrated into individual ICs, they interface according to a UTMI (USB 2.0 Transceiver Macro Interface) specification. Further, a ULPI (UTMI+Low Pin Interface) specification, which is an extended version of the UTMI specification, is also available. According to the UTMI specification, interface transmission speeds of 60 MHz×8 bits, and 30 MHz×16 bits are available for selection. Further, according to the ULPI specification, the interface transmission speed is 60 MHz×8 bits.
A problem to solve when developing a USB controller device is concerned with testing the device at a high speed. As described above, the communication bit rate of the USB 2.0 is 480 Mbps (=8 bits×60 MHz). For testing the IC at this high speed, a very expensive test jig is necessary. Therefore, in a manufacturing process of the IC, logic testing is often excluded to dispense with the costly test jig, and the IC is mounted on an evaluation board or the like so that functional testing of operations may be performed. If inferior goods can be eliminated at an early stage of a testing process in manufacturing, it is possible to eliminate unnecessary man-hours and cost of testing.
In this view, various techniques have been disclosed in an attempt to improve testing efficiency of IC operations at the high-speed communications.
For example, Patent Reference 1 discloses a communication device that is capable of detecting an abnormality of a transceiver in communications state close to real operations wherein a frequency error, transmission jitter, clock waveform fluctuation, and phase-angle fluctuation are added by a loop-back operation for reducing the testing cost. Here, evaluation of internal DRC (Design Rule Check), an elastic buffer, and a decoder are carried out by changing timing by a phase-adjustment (clock modulation) unit, and the like. Further, Patent Reference 2 discloses a USB device controller that can satisfy restrictions of an inter-packet delay time in the USB specification with a small-scale circuit.
[Patent reference 1] JPA 2004-260677
[Patent reference 2] JPA 2004-021742